Superhard constructions and methods of making same

ABSTRACT

A polycrystalline super hard construction has a first region having a body of thermally stable polycrystalline super hard material having a plurality of intergrown grains of super hard material; a second region forming a substrate having a hard phase and a binder phase; and a third region interposed between the first and second regions. The third region includes a composite material having a first phase comprising a plurality of non-intergrown grains of super hard material, and a matrix material. A fourth region interposed between the second and third region has a major proportion having one or more components of the binder material of the second region, and one or more reaction products between the binder material of the second region and one or more components of the third region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the § 371 national stage of InternationalApplication No. PCT/EP2017/084718, filed Dec. 28, 2017, which claimspriority to Great Britain Application No. 1622455.2, filed Dec. 31,2016.

FIELD

This disclosure relates to super hard constructions and methods ofmaking such constructions, particularly but not exclusively toconstructions comprising polycrystalline diamond (PCD) structuresattached to a substrate, and tools comprising the same, particularly butnot exclusively for use in rock degradation or drilling, or for boringinto the earth.

BACKGROUND

Polycrystalline super hard materials, such as polycrystalline diamond(PCD) and polycrystalline cubic boron nitride (PCBN) may be used in awide variety of tools for cutting, machining, drilling or degrading hardor abrasive materials such as rock, metal, ceramics, composites andwood-containing materials. In particular, tool inserts in the form ofcutting elements comprising PCD material are widely used in drill bitsfor boring into the earth to extract oil or gas. The working life ofsuper hard tool inserts may be limited by fracture of the super hardmaterial, including by spalling and chipping, or by wear of the toolinsert.

Cutting elements such as those for use in rock drill bits or othercutting tools typically have a body in the form of a substrate which hasan interface end/surface and a super hard material which forms a cuttinglayer bonded to the interface surface of the substrate by, for example,a sintering process. The substrate is generally formed of a tungstencarbide-cobalt alloy, sometimes referred to as cemented tungsten carbideand the super hard material layer is typically polycrystalline diamond(PCD), polycrystalline cubic boron nitride (PCBN) or a thermally stableproduct TSP material such as thermally stable polycrystalline diamond.

Polycrystalline diamond (PCD) is an example of a super hard material(also called a superabrasive material or ultra hard material) comprisinga mass of substantially inter-grown diamond grains, forming a skeletalmass defining interstices between the diamond grains. PCD materialtypically comprises at least about 80 volume % of diamond and isconventionally made by subjecting an aggregated mass of diamond grainsto an ultra-high pressure of greater than about 5 GPa, and temperatureof at least about 1,200° C., for example. A material wholly or partlyfilling the interstices may be referred to as filler or binder material.

PCD is typically formed in the presence of a sintering aid such ascobalt, which promotes the inter-growth of diamond grains. Suitablesintering aids for PCD are also commonly referred to as asolvent-catalyst material for diamond, owing to their function ofdissolving, to some extent, the diamond and catalysing itsre-precipitation. A solvent-catalyst for diamond is understood be amaterial that is capable of promoting the growth of diamond or thedirect diamond-to-diamond inter-growth between diamond grains at apressure and temperature condition at which diamond is thermodynamicallystable. Consequently the interstices within the sintered PCD product maybe wholly or partially filled with residual solvent-catalyst material.Most typically, PCD is often formed on a cobalt-cemented tungstencarbide substrate, which provides a source of cobalt solvent-catalystfor the PCD.

Ever increasing drives for improved productivity in the earth boringfield place ever increasing demands on the materials used for cuttingrock. Specifically, PCD materials with improved abrasion and impactresistance are required to achieve faster cut rates and longer toollife.

One of the factors limiting the success of the polycrystalline diamond(PCD) abrasive cutters particularly when used as cutting elements indrill bits for boring into the earth in the oil and gas drillingindustry is the generation of heat due to friction between the PCD andthe work material. This heat causes the thermal degradation of thediamond layer. The thermal degradation increases the wear rate of thecutter through increased cracking and spalling of the PCD layer as wellas back conversion of the diamond to graphite causing increased abrasivewear. In particular, the high temperatures incurred during operationcause the residual binder-catalyst, e.g. cobalt, in the diamond matrixto thermally expand. This thermal expansion is known to cause thediamond crystalline bonds within the microstructure to be broken at ornear the cutting edge, thereby also operating to reduce the life of thePCD cutter. Also, in high temperature cutting environments, the cobaltin the PCD matrix can facilitate the conversion of diamond back tographite, which is also known to radically decrease the performance lifeof the cutting element.

Attempts in the art to address the above-noted limitations have largelyfocused on the solvent catalyst material's degradation of the PCDconstruction by catalytic operation, and removal of the catalystmaterial therefrom for the purpose of enhancing the working life of PCDcutting elements. For example, it is known to treat the PCD body toremove the solvent catalyst material therefrom. One known way of doingthis involves removing the solvent catalyst material for example by anacid leaching process. To obtain the maximum benefit, ideally all of theaccessible residual solvent catalyst should be removed from the PCDmaterial however, there are many examples in the prior art thatacknowledge the extreme difficulty and problems associated in practicewith fully leaching the PCD material of such residual solvent catalyst.Firstly, it is known that removing substantially all of the residualcatalyst-binder from the interstitial spaces weakens the PCD material byas much as 30% so whilst the abrasion resistance of such a PCD compositemay be improved there is a significant decrease in impact resistance ofthe composite which reduces the working life of the composite. Secondly,the substrate portion of the composite which is typically formed oftungsten carbide is particularly vulnerable to attack and degradation bythe acid used in techniques such as acid leaching. This is particularlyproblematic if the interface between the PCD region and the substrate isnon planar as protruding interface features in the carbide materialwould be subject to attack from the acid during the leaching processthereby weakening the bond between the PCD material and substrate whichcould reduce the working life of the element.

To address these problems, various leaching profiles have been developedto remove solvent catalyst material only from specific regions in thePCD material leaving an amount of residual catalyst in the PCD material,particularly along the interface with the substrate to preserve the bondtherebetween. However, as mentioned above, leaving residual catalystsolvent in the cutting element does not eliminate the problemsassociated with thermal degradation due to the mismatch in coefficientsof thermal expansion between the diamond grains and solvent catalyst.

Another solution proposed in the art if it is desired to remove all ofthe residual solvent catalyst from the PCD material, is to attach a newsubstrate to the TS PCD once leached prior to use as a cutting element.This is typically required due to the vulnerability of the tungstencarbide substrate to attack and degradation by the acid used in theconventional leaching techniques. However, a difficulty also known toexist with such TS PCD is the challenge associated with attaching the TSbody to a new substrate to form a usable compact. Not only are thereproblems in achieving a join that has sufficient strength to withstandthe extreme working conditions such as in drilling applications but alsoforming such a join has typically only been possible with planarinterfaces between such pieces. This itself results in residual stressproblems between the joined materials in application thereby impactingthe working life of the compact.

Additionally, past attempts made to attach such TS PCD to a substrate byan HPHT process have resulted in crack formation in the TS PCD and/ordelamination between the substrate and TS PCD body during use, making itunsuitable for use in a cutting and/or wear environment. Such crackformation is even more problematic when attempting to attach TS PCD to asubstrate where the interface between the two is nonplanar and thereforehas not typically been deemed viable.

It is, therefore, desirable that a thermally stable polycrystallinediamond construction be engineered in a manner that not only displaysimproved thermal characteristics, when compared to conventional PCD, butalso has improved fracture toughness without adversely affecting thematerial's high strength and abrasion resistance.

SUMMARY

Viewed from a first aspect there is provided a polycrystalline superhard construction comprising:

-   -   a first region comprising a body of thermally stable        polycrystalline super hard material having an exposed surface        forming a working surface, and a peripheral side edge, said        polycrystalline super hard material comprising a plurality of        intergrown grains of super hard material;    -   a second region forming a substrate to the first region, the        second region comprising a hard phase and a binder phase;    -   a third region interposed between the first and second regions,        the third region extending across a surface of the second region        along an interface; wherein    -   the third region comprises a composite material having a first        phase comprising a plurality of non-intergrown grains of super        hard material, and a matrix material;        the super hard polycrystalline construction further comprising a        fourth region interposed between the second region and the third        region, a major proportion of the fourth region comprising one        or more components of the binder material of the second region,        the fourth region further comprising one or more reaction        products between the binder material of the second region and        one or more components of the third region.

Viewed from a second aspect there is provided a method of forming asuper hard polycrystalline construction comprising:

-   -   forming a pre-sinter assembly comprising:    -   a first mass of grains or particles of a super hard material;    -   a source of catalysing material for the first mass of grains or        particles of super hard material;    -   a further mass of grains or particles of a super hard material        mixed with grains or particles of a non-super hard material; and    -   a mass of grains or particles of a material to form a substrate;    -   treating the pre-sinter assembly at an ultra-high pressure of        around 5 GPa or greater and a temperature to bond together the        grains of super hard material in the first mass to form a first        region comprising a body of interbonded polycrystalline super        hard material bonded to an intermediate region formed of        substantially non-interbonded grains or particles of the super        hard material in the further mass; the intermediate region being        bonded to a further region along an interface which is bonded to        the substrate comprising a hard phase and a binder material        along a further interface, one or other or both of the        interfaces comprising at least a portion having an uneven        topology, the intermediate region between the first region and        the further region comprising:    -   a composite material including:    -   a first region comprising a first phase comprising a plurality        of non-intergrown grains of super hard material,    -   a matrix material;    -   a major proportion of the further region interposed between the        substrate and the intermediate region fourth region comprising        one or more components of the binder material of the substrate,        the further region further comprising one or more reaction        products between the binder material of the substrate and one or        more components of the intermediate region.

Viewed from a further aspect there is provided a tool comprising thesuper hard polycrystalline construction defined above, the tool beingfor cutting, milling, grinding, drilling, earth boring, rock drilling orother abrasive applications.

The tool may comprise, for example, a drill bit for earth boring or rockdrilling, a rotary fixed-cutter bit for use in the oil and gas drillingindustry, or a rolling cone drill bit, a hole opening tool, anexpandable tool, a reamer or other earth boring tools.

Viewed from another aspect there is provided a drill bit or a cutter ora component therefor comprising the super hard polycrystallineconstruction defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

Various versions will now be described by way of example and withreference to the accompanying drawings in which:

FIG. 1 is a perspective view of an example of a conventional PCD cutterelement or construction for a drill bit for boring into the earth;

FIG. 2 is a schematic cross-section of a conventional portion of a PCDmicro-structure with interstices between the inter-bonded diamond grainsfilled with a non-diamond phase material;

FIG. 3 is a schematic cross-section of a first example of a super hardconstruction;

FIG. 4 is a schematic cross-section of a second example of a super hardconstruction;

FIG. 5 is a schematic cross-section of a third example of a super hardconstruction;

FIG. 6 is a schematic cross-section of a fourth example of a super hardconstruction;

FIG. 7 is a schematic plan view of the super hard construction of FIG. 5;

FIG. 8 is a schematic plan view of the super hard construction of FIG. 6;

FIG. 9 is a is a schematic alternative plan view of the super hardconstruction of FIG. 5 ;

FIG. 10 is a schematic cross-section of a sixth example of a super hardconstruction; and

FIG. 11 is a plot showing the results of a vertical borer test comparingthe material of the intermediate region of an example with twoconventional PCD cutter elements;

FIG. 12 is a plot showing the results of a vertical borer test for anexample super hard construction; and

FIG. 13 is a plot showing the results of a vertical borer test comparingan example super hard construction with three conventional PCD cutterelements.

The same references refer to the same general features in all thedrawings.

DESCRIPTION

As used herein, a “super hard material” is a material having a Vickershardness of at least about 28 GPa. Diamond and cubic boron nitride (cBN)material are examples of super hard materials.

As used herein, a “super hard construction” means a constructioncomprising a body of polycrystalline super hard material. In such aconstruction, a substrate may be attached thereto.

As used herein, polycrystalline diamond (PCD) is a type ofpolycrystalline super hard (PCS) material comprising a mass of diamondgrains, a substantial portion of which are directly inter-bonded(intergrown) with each other and in which the content of diamond is atleast about 80 volume percent of the material. In one example of PCDmaterial, directly after sintering, interstices between the diamondgrains may be at least partly filled with a binder material comprising acatalyst for diamond. As used herein, “interstices” or “interstitialregions” are regions between the diamond grains of PCD material.

A “catalyst material” for a super hard material is capable of promotingthe growth or sintering of the super hard material.

The term “substrate” as used herein means any substrate over which thesuper hard material layer is formed. For example, a “substrate” as usedherein may be a transition layer formed over another substrate.

As used herein, the term “integrally formed” means regions or parts areproduced contiguous with each other and are not separated by a differentkind of material.

As used herein, the term “super hard composite” means a compositematerial formed of substantially non-intergrown grains of super hardmaterial in a matrix of binder phase material, for example less than 3%of the grains of super hard material are intergrown, and in someinstances none of the super hard grains are intergrown. Whether or notthe super hard grains are intergrown may be determined usingconventional methods of SEM or X-ray analysis of images taken of theconstruction. In addition, for a substantially non-intergrown structure,the wear resistance of the material will be substantially less (that is,worse) than sintered polycrystalline diamond material having the sameaverage grain size of diamond grains as the super hard grains in thecomposite structure. This may be confirmed using conventional tests suchas a vertical borer test of the material.

FIG. 1 is a schematic view of an example of a conventional PCD superhard construction such as a cutting element 1 which includes a substrate3 with a layer of super hard material 2 formed on the substrate 3. Thesubstrate 3 may be formed of a hard material such as cemented tungstencarbide. The super hard material 2 may be, for example, high densitypolycrystalline diamond (PCD) comprising at least 80 vol % ofinterbonded (intergrown) diamond grains. The cutting element 1 may bemounted into a bit body such as a drag bit body (not shown) and may besuitable, for example, for use as a cutter insert for a drill bit forboring into the earth.

The exposed top surface of the super hard material opposite thesubstrate forms the cutting face 4, also known as the working surface,which is the surface which, along with its edge 6, performs the cuttingin use.

At one end of the substrate 3 is an interface surface 8. As shown inFIG. 1 , the substrate 3 is generally cylindrical and has a peripheralsurface 10 and a peripheral top edge 12.

The working surface or “rake face” 4 of the polycrystalline compositeconstruction 1 is the surface or surfaces over which the chips ofmaterial being cut flow when the cutter is used to cut material from abody, the rake face 4 directing the flow of newly formed chips. Thisface 4 is commonly also referred to as the top face or working surfaceof the cutting element as the working surface 4 is the surface which,along with its edge 6, is intended to perform the cutting of a body inuse. It is understood that the term “cutting edge”, as used herein,refers to the actual cutting edge, defined functionally as above, at anyparticular stage or at more than one stage of the cutter wearprogression up to failure of the cutter, including but not limited tothe cutter in a substantially unworn or unused state.

As used herein, “chips” are the pieces of a body removed from the worksurface of the body being cut by the polycrystalline compositeconstruction 1 in use.

As used herein, a “wear scar” is a surface of a cutter formed in use bythe removal of a volume of cutter material due to wear of the cutter. Aflank face may comprise a wear scar. As a cutter wears in use, materialmay progressively be removed from proximate the cutting edge, therebycontinually redefining the position and shape of the cutting edge, rakeface and flank as the wear scar forms.

The substrate 3 is typically formed of a hard material such as acemented carbide material, for example, cemented tungsten carbide.

As shown in FIG. 2 , during formation of a conventional polycrystallinecomposite construction 1′ comprising a body of polycrystalline superhard material 2′ bonded to a substrate 3′, the interstices 24 betweenthe inter-bonded grains 22 of super hard material such as diamond grainsin the case of PCD, may be at least partly filled with a non-super hardphase material. This non-super hard phase material, also known as afiller material may comprise residual catalyst/binder material, forexample cobalt.

FIGS. 3 to 10 are schematic cross-sections through examples of superhard constructions which may have the same outer shape as theconstruction 1 of FIG. 1 .

In a first example, as shown in FIG. 3 , the super hard construction 30includes a layer or region of super hard material 34 forming the rakeface or cutting surface 4 and having the cutting edge 6, a substrate 32and a region 36 intermediate the layer of super hard material 34 and thesubstrate 32. The interface 37 between the substrate and theintermediate region 36 has at least a portion having an uneven topology.This may be interpreted as, but not limited to, covering one or more ofthe surface being non-uniform, varying, irregular, rugged, not level,and/or not smooth, and/or with peaks and troughs. Additionally, in theexample shown in FIG. 3 , the interface 38 between the layer of superhard material 34 and the intermediate region 36 is substantiallynon-planar. The intermediate region 36 has a further region 39 extendingalong the interface with the substrate 32. The further region 39 may,for example, be formed during the sintering process between thesubstrate 32 and the intermediate region 36, and a major proportion ofthe further region 39 may comprise one or more components of the bindermaterial of the substrate 32 and one or more reaction products betweenthe binder material of the substrate 32 and one or more components ofthe intermediate region 36.

One or other or both of the interfaces between the intermediate region36 and the region of super hard material 34 and the intermediate region36 and the substrate 32 may have at least a portion having an uneventopology.

In the example of FIG. 3 , the intermediate region 36 does not form partof the working surface but is spaced therefrom by a region of the superhard material 34. Additionally, the intermediate region 36 of super hardcomposite material extends across the interface 37 with the substrate 32and spaces the super hard layer 34 from the substrate 32.

The example of a super hard construction 40 shown in FIG. 4 differs fromthat shown in FIG. 3 in that the interface 48 between the layer of superhard material 44 and the intermediate region 46 is substantially planar.The interface between the intermediate region 46, and the further region49 and the interface 47 between the further region 49 with the substrateare shown as having at least a portion which is uneven.

The further example of a super hard construction 50 shown in FIG. 5differs from that shown in FIG. 3 in that an intermediate region 56 of acomposite material formed of non-interbonded grains of super hardmaterial, such as diamond grains, that is interposed between a substrate52 and layer of super hard material 54 extends to and forms part of theworking surface 4 of the super hard construction 50. The interface 57between the further region 59 and the substrate 52 and the intermediateregion 56 and the further region 59 has at least a portion having anuneven topology and the interface 58 between the intermediate region 56and the layer of super hard material 54 is also substantiallynon-planar, the interface 58 being concavely arcuate.

FIG. 6 is an example similar to that shown in FIG. 5 with the exceptionthat the interface 68 between the region or layer of polycrystallinesuper hard material 64 and the intermediate region 66 is slopedoutwardly from the working surface towards the substrate 62 rather thanconcavely curved, and that is shown by the inclined plane depicted in incross section in FIG. 6 , the intermediate region 66 thereby comprisinga truncated cone projecting from the substrate 62 and extending throughthe layer or region of super hard material 64 to the cutting face,forming part of the working surface of the super hard construction 60.Additionally, the further region 69 extends across the interface 67 withthe substrate 62.

FIG. 7 shows the example construction of FIG. 5 in plan view and it willbe seen that the super hard region or layer 54 forms an annular portionaround the outer peripheral surface of the intermediate region ofcomposite material 56.

As shown in the plan views, FIGS. 7 and 8 , of the examples of FIGS. 5and 6 respectively, the super hard layer or region 54 may form anannular portion around the outer peripheral surface of the intermediateregion 56 of composite material, or the layer or region of super hardmaterial 64 may be in the form of segments interposed around the cuttingedge with the intermediate region 64. The advantage of such aconstruction may be that the construction may be rotatable after usesuch that a different cutting edge may be presented to the surface to becut and also the segments may act to confine damage to a limited area ofthe construction during use.

In some examples, such as that shown in FIG. 9 , and in particular thosewhere the intermediate region 74 extends to and forms part of thecutting face 4, the interface 76 between the intermediate region 74 andthe layer of super hard material 72 may be ridged or grooved, suchridges or grooves extending, for example, from the cutting face 4 to theflank face of the construction.

In some examples (not shown), the intermediate region may have thegeneral structure of that shown in FIGS. 5 and 6 but may not extend allthe way to or form part of the working surface. For example, theintermediate region may extend to a distance of around 0.5 mm or lessfrom the working surface.

In the further example shown in FIG. 10 , the super hard construction 90comprises a substrate 92, a layer of super hard material 94 and anintermediate region 96 between the layer of super hard material 94 andthe substrate 92, a further region 99 spacing the intermediate region 96and the layer of super hard material 94 from the substrate 92. Theinterface 97 between the substrate and the further region 99 has atleast a portion having an uneven topology and the interface 98 betweenthe intermediate region 96 and the layer of super hard material 94 isalso substantially non-planar, and may comprise one or more grooves orridges to provide an interlocking fit between the two layers.

In some examples, the further region 39, 49, 59, 69, 79, 99 may, forexample, be formed during the sintering process between the substrateand the intermediate region, and a major proportion of the furtherregion may comprise one or more components of the binder material of thesubstrate and one or more reaction products between the binder materialof the substrate and one or more components of the intermediate region.

In one or more of the examples, such as those shown in any one or moreof FIGS. 3 to 10 , the layer or region of super hard material 34, 44,54, 64, 74, 94, prior to final processing and directly after sintering,may for example have a micro-structure with interstices between theinter-bonded grains of super hard material filled with a non-super hardphase material such as that shown in the representation of conventionalPCD in FIG. 2 . However, in the end product, in the case of the superhard grains being diamond, the interstitial spaces between inter-bondeddiamond grains are substantially free of accessible residual solventcatalyst that would otherwise be present in the interstitial spaces andthe layer or region of super hard material 34, 44, 54, 64, 74, 94, isconsidered to be fully leached thermally stable PCD.

The super hard material of the various examples used to form the layeror region of super hard material 34, 44, 54, 64, 74, 94, may be, forexample, polycrystalline diamond (PCD) and/or polycrystalline cubicboron nitride (PCBN) and/or lonsdalite and the super hard particles orgrains may be of natural and/or synthetic origin.

The substrate of the examples, 32, 42, 52, 62, 72, 92 may be formed of ahard material such as a cemented carbide material and may include, forexample, cemented tungsten carbide, cemented tantalum carbide, cementedtitanium carbide, cemented molybdenum carbide or mixtures thereof. Thebinder metal for such carbides suitable for forming the substrate 32,42, 52, 62, 72, 92 may be, for example, nickel, cobalt, iron or an alloycontaining one or more of these metals and may include additionalelements or compounds of other materials such as chromium, or vanadium.This binder may, for example, be present in an amount of 10 to 20 mass%, but this may be as low as 6 mass % or less.

In some examples, the layer or region of polycrystalline super hardmaterial 34, 44, 54, 64, 74, 94, may be a high density PCD formed ofmore than 95 vol % of diamond. Such a PCD body may be formed using knownmethods such as by sintering the diamond grains at sintering pressuresof around 8 GPa and above, as described in US patent applicationpublished as US 2010/0084196.

In some examples, the layer or region of polycrystalline super hardmaterial 34, 44, 54, 64, 74, 94, may be formed of high density PCDcomprising a sintered mass of nano diamond grains as set out in USpatent application published as US2005/019114.

In some examples, high density or binderless PcBN, and PcBNconstructions formed from nanomaterials may also be formed according toknown methods.

In some examples, the layer or region of super hard material 34, 44, 54,64, 74, 94, may comprise PCBN. Components comprising PCBN are usedprincipally for machining metals. PCBN material comprises a sinteredmass of cubic boron nitride (cBN) grains. The cBN content of PCBNmaterials may be at least about 40 volume %. When the cBN content in thePCBN is at least about 70 volume % there may be substantial directcontact among the cBN grains. When the cBN content is in the range fromabout 40 volume % to about 60 volume % of the compact, then the extentof direct contact among the cBN grains is limited. PCBN may be made bysubjecting a mass of cBN particles together with a powdered matrixphase, to a temperature and pressure at which the cBN isthermodynamically more stable than the hexagonal form of boron nitride,hBN. PCBN is less wear resistant than PCD which may make it suitable fordifferent applications to that of PCD.

As used herein, a PCD or PCBN grade is a PCD or PCBN materialcharacterised in terms of the volume content and size of diamond grainsin the case of PCD or cBN grains in the case of PCBN, the volume contentof interstitial regions between the grains, and composition of materialthat may be present within the interstitial regions. A grade of superhard material may be made by a process including providing an aggregatemass of super hard grains having a size distribution suitable for thegrade, optionally introducing catalyst material or additive materialinto the aggregate mass, and subjecting the aggregated mass in thepresence of a source of catalyst material for the super hard material toa pressure and temperature at which the super hard grains are morethermodynamically stable than graphite (in the case of diamond) or hBN(in the case of CBN), and at which the catalyst material is molten.Under these conditions, molten catalyst material may infiltrate from thesource into the aggregated mass and is likely to promote directintergrowth between the diamond grains in a process of sintering, toform a polycrystalline super hard structure. The aggregate mass maycomprise loose super hard grains or super hard grains held together by abinder material. In the context of diamond, the diamond grains may benatural or synthesised diamond grains.

Different grades of super hard material such as polycrystalline diamondmay have different microstructures and different mechanical properties,such as elastic (or Young's) modulus E, modulus of elasticity,transverse rupture strength (TRS), toughness (such as so-called K₁Ctoughness), hardness, density and coefficient of thermal expansion(CTE). Different PCD grades may also perform differently in use. Forexample, the wear rate and fracture resistance of different PCD gradesmay be different.

The layer or region 34, 44, 54, 64, 74, 94, of polycrystalline superhard material shown in the cutter elements 30, 40, 50, 60, 70, 90 ofFIGS. 3 to 10 may comprise, for example, one or more grades of superhard material and may comprise one or more layers of super hard materialwhich may differ in, for example, grain size and/or composition of thesuper hard material.

In particular, the grains of super hard material may be, for example,diamond grains or particles. In the starting mixture prior to sinteringthey may be, for example, bimodal, that is, the feed comprises a mixtureof a coarse fraction of diamond grains and a fine fraction of diamondgrains. In some embodiments, the coarse fraction may have, for example,an average particle/grain size ranging from about 10 to 60 microns. By“average particle or grain size” it is meant that the individualparticles/grains have a range of sizes with the mean particle/grain sizerepresenting the “average”. The average particle/grain size of the finefraction is less than the size of the coarse fraction. For example, thefine fraction may have an average grain size of between around 1/10 to6/10 of the size of the coarse fraction, and may, in some embodiments,range for example between about 0.1 to 20 microns.

In some examples, the weight ratio of the coarse diamond fraction to thefine diamond fraction may range from about 50% to about 97% coarsediamond and the weight ratio of the fine diamond fraction may be fromabout 3% to about 50%. In other embodiments, the weight ratio of thecoarse fraction to the fine fraction may range from about 70:30 to about90:10.

In further examples, the weight ratio of the coarse fraction to the finefraction may range for example from about 60:40 to about 80:20.

In some examples, the particle size distributions of the coarse and finefractions do not overlap and in some embodiments the different sizecomponents of the compact are separated by an order of magnitude betweenthe separate size fractions making up the multimodal distribution.

Some examples consist of a wide bi-modal size distribution between thecoarse and fine fractions of super hard material, but some examples mayinclude three or even four or more size modes which may, for example, beseparated in size by an order of magnitude, for example, a blend ofparticle sizes whose average particle size is 20 microns, 2 microns, 200nm and 20 nm.

Sizing of diamond particles/grains into fine fraction, coarse fraction,or other sizes in between, may be through known processes such asjet-milling of larger diamond grains and the like.

In some examples, the cemented metal carbide substrate 32, 42, 52, 62,72, 92 may, for example, be conventional in composition and, thus, mayinclude any of the Group IVB, VB, or VIB metals, which are pressed andsintered in the presence of a binder of cobalt, nickel or iron, oralloys thereof. In some examples, the metal carbide is tungsten carbide.

The intermediate region 36, 46, 56, 66, 76, 96 is a composite materialformed of non-interbonded grains of super hard material, such as diamondgrains, and a matrix material. In some examples, the matrix materialfurther comprises a second phase such as a material that has a lowerhardness than the hardness of the super hard grains. The additional hardmaterial may, for example be any one or more of cBN, WC, wBN and thelike. In some examples the matrix material of the intermediate regioncomprises any one or more alloys or compounds of any one or moretransition metals including titanium, zirconium, vanadium, hafnium,tantalum, niobium, chromium, molybdenum, tungsten, copper, cobalt,nickel, iron, manganese, and/or rhenium. The one or more alloys orcompounds may, for example be any one or more oxides, nitrides,carbides, carbonitrides, and/or oxycarbides of said transition metals.In some examples, the matrix material comprises aluminium, and/or nickeland/or one or more alloys or compounds thereof.

In further examples, the matrix material of the intermediate regioncomprises any one or more of titanium carbonitride, titanium diboride,aluminium nitride, aluminium oxide, cobalt, and tungsten carbide, oralloys or compounds thereof.

In some examples, the matrix material comprises between around 5 vol %to around 80 vol % of the material of the intermediate region, and insome examples comprises between around 5 to 60 vol % thereof, or betweenaround 10 vol % to around 30 vol % thereof.

In some examples, the super hard grains in the intermediate regioncomprise between around 30 vol % to around 70 vol % of the material ofthe intermediate region.

In some examples, the grains of super hard material in the intermediateregion together with any additional phase to the matrix materialcomprises between around 20 vol % to around 95 vol % of the material ofthe intermediate region, and in some examples may be between around 70vol % to around 90 vol % thereof, or between around 50 vol % to around90 vol % thereof, or between around 30 vol % to around 90 vol % thereof.

The materials forming the layer or region of super hard material, theintermediate region and the substrate all have an associated hardnessand, in some examples, the hardness of the intermediate region isgreater than the hardness of the substrate and less than the hardness ofthe layer or region of super hard material.

In some examples, the intermediate region may comprise two or more layeror regions differing in composition and/or construction, such asmultiple layers of composite material having at least the characteristicof non intergrown or interbonded grains of super hard material and amatrix material.

The depth of the layer or region of super hard material 34, 44, 54, 64,74, 94 from the working surface along the peripheral side edge of therespective construction 30, 40, 50, 60, 70, 90 may, for example, be atleast around 0.3 mm or greater, such as between around 0.3 mm to around6.5 mm. Additionally, in some embodiments, the thickness of theintermediate region 36, 46, 56, 66, 76, 96 along a plane parallel to thelongitudinal axis of the construction may be at least 0.05 mm, forexample between around 0.1 mm to around 4 mm, between around 0.3 toaround 1 mm, or between around 0.5 mm to around 0.8 mm.

In any one or more examples, the concentration of super hard grains inthe intermediate region may be graded from the interface with the layeror region of super hard material to the substrate.

Furthermore, in some examples, the layer or region of super hardmaterial comprises substantially no constituents of the matrix materialof the intermediate region.

In the super hard polycrystalline constructions according to any one ormore of the examples, the layer or region of super hard material 34, 44,54, 64, 72, 84, 94 comprises a thermally stable material such asthermally stable PCD, and, if the super hard material comprises diamondgrains, may have a diamond content between around 80 volume % to around100 volume %. The thermally stable layer of super hard material may, forexample, be substantially free of all accessible catalyst material fordiamond, said region forming the thermally stable first region, and may,for example comprise at most around 3 weight percent of catalystmaterial for diamond.

In some examples, the layer of thermally stable super hard materialcomprises binderless PCD material and/or CVD diamond and/or apolycrystalline super hard material formed from nanodiamond grains.

In any one or more examples, the intermediate region 36, 46, 56, 66, 86,96 may be bonded to the layer of super hard material and/or to a furtherintermediate region, and/or to the substrate 32, 42, 52, 62, 82, 92 by abrazed joint and/or a sintered joint along the respective interfaces.

The grains of super hard material used for making the thermally stablesuper hard layer 34, 44, 54, 64, 84, 94 may be, for example, diamondgrains or particles, or for example, lonsdalite or cBN grains orparticles. As mentioned above, in the starting mixture prior tosintering they may be, for example, bimodal, that is, the feed comprisesa mixture of a coarse fraction of super hard grains and a fine fractionof super hard grains.

In some examples, the binder catalyst/solvent used to assist in thebonding of the grains of super hard material such as diamond grains inthe sintering process, may comprise cobalt or some other iron groupelements, such as iron or nickel, or an alloy thereof. Carbides,nitrides, borides, and oxides of the metals of Groups IV-VI in theperiodic table are other examples of non-diamond material that might beadded to the sinter mix. In some examples, the binder/catalyst/sinteringaid may be Co.

The super hard constructions of the examples shown in FIGS. 3 to 10 maybe fabricated, for example, as follows.

The substrate and intermediate region(s) may be pre-formed. In someexamples, the substrate may be pre-formed by pressing the green body ofgrains of hard material such as tungsten carbide into the desired shape,including the interface features at one free end thereof, and sinteringthe green body to form the substrate element. In an alternative example,the substrate interface features may be machined from a sinteredcylindrical body of hard material, to form the desired geometry for theinterface features. The substrate may, for example, comprise WCparticles bonded with a catalyst material such as cobalt, nickel, oriron, or mixtures thereof. A green body for the super hard construction,which comprises the pre-formed substrate, the pre-formed intermediateregion and the particles of super hard material such as diamondparticles or cubic boron nitride particles, may be placed onto thesubstrate, to form a pre-sinter assembly which may be encapsulated in acapsule for an ultra-high pressure furnace, as is known in the art. Inparticular, the superabrasive particles, for example in powder form, areplaced inside a metal cup formed, for example, of niobium, tantalum, ortitanium. The pre-formed substrate and intermediate region are placedinside the cup and hydrostatically pressed into the super hard powdersuch that the requisite powder mass is pressed around the interfacefeatures of the preformed carbide substrate to form the pre-composite.The pre-composite is then outgassed at about 1050 degrees C. Thepre-composite is closed by placing a second cup at the other end and thepre-composite is sealed by cold isostatic pressing or EB welding. Thepre-composite is then sintered to form the sintered body.

In some examples, the super hard grains may be diamond grains and thesubstrate may be cobalt-cemented tungsten carbide. The pre-sinterassembly may comprise an additional source of catalyst material such asa disc containing catalyst material such as cobalt which may be placedadjacent the diamond grains in the pre-composite assembly.

In some examples, the binder catalyst/solvent used in the initialpre-sinter mixture may comprise cobalt or some other iron groupelements, such as iron or nickel, or an alloy thereof. Carbides,nitrides, borides, and oxides of the metals of Groups IV-VI in theperiodic table are other examples of non-diamond material that might beadded to the sinter mix. In some examples, the binder/catalyst/sinteringaid may be Co.

In one example, the method may include loading the capsule comprising apre-sinter assembly into a press and subjecting the green body to anultra-high pressure and a temperature at which the super hard materialis thermodynamically stable to sinter the super hard grains. In someexamples, the green body may comprise diamond grains and the pressure towhich the assembly is subjected is at least about 5 GPa and thetemperature is at least about 1,300 degrees centigrade. In someexamples, the pressure to which the assembly may be subjected is around5.5-6 GPa, but in some examples it may be around 7.7 GPa or greater.Also, in some examples, the temperature used in the sintering processmay be in the range of around 1400 to around 1500 degrees C.

After sintering, the polycrystalline super hard constructions may beground to size and may include, if desired, a 45° chamfer of, forexample, approximately 0.4 mm height on the body of polycrystallinesuper hard material so produced.

Solvent/catalyst for diamond may be introduced into the aggregated massof diamond grains by various methods, including admixing or blendingsolvent/catalyst material in powder form with the diamond grains,depositing solvent/catalyst material onto surfaces of the diamondgrains, or infiltrating solvent/catalyst material into the aggregatedmass from a source of the material, either prior to the sintering stepor as part of the sintering step. Methods of depositing solvent/catalystfor diamond, such as cobalt, onto surfaces of diamond grains are wellknown in the art, and include chemical vapour deposition (CVD), physicalvapour deposition (PVD), sputter coating, electrochemical methods,electroless coating methods and atomic layer deposition (ALD). It willbe appreciated that the advantages and disadvantages of each depend onthe nature of the sintering aid material and coating structure to bedeposited, and on characteristics of the grain.

In one example, the binder/catalyst such as cobalt may be deposited ontosurfaces of the diamond grains by first depositing a pre-cursor materialand then converting the precursor material to a material that compriseselemental metallic cobalt. For example, in the first step cobaltcarbonate may be deposited on the diamond grain surfaces using thefollowing reaction:Co(NO₃)₂+Na₂CO₃→CoCO₃+2NaNO₃

The deposition of the carbonate or other precursor for cobalt or othersolvent/catalyst for diamond may be achieved by means of a methoddescribed in PCT patent publication number WO/2006/032982. The cobaltcarbonate may then be converted into cobalt and water, for example, bymeans of pyrolysis reactions such as the following:CoCO₃→CoO+CO₂CoO+H₂→CO+H₂O

In another example, cobalt powder or precursor to cobalt, such as cobaltcarbonate, may be blended with the diamond grains. Where a precursor toa solvent/catalyst such as cobalt is used, it may be necessary to heattreat the material in order to effect a reaction to produce thesolvent/catalyst material in elemental form before sintering theaggregated mass.

In some examples, the cemented carbide substrate may be formed oftungsten carbide particles bonded together by the binder material, thebinder material comprising an alloy of Co, Ni and Cr. The tungstencarbide particles may form at least 70 weight percent and at most 95weight percent of the substrate. The binder material may comprisebetween about 10 to 50 wt. % Ni, between about 0.1 to 10 wt. % Cr, andthe remainder weight percent comprises Co.

Examples are described in more detail below with reference to thefollowing which are provided herein by way of illustration only and arenot intended to be limiting.

EXAMPLE 1

The super hard constructions of FIGS. 3 to 10 may be formed as follows.

A preformed structure which is to form the intermediate region was madeby first forming a non-diamond phase mixture comprising titaniumcarbonitride and aluminium powders, the TiCN forming around 90 vol % ofthe non-diamond phase mixture and the Al powder forming around 10 vol %of the non-diamond phase mixture. The stoichiometric ratio of C:N in theTiCN was 0.5:0.5 (with a 90:10 wt % ratio). The average grain size ofthe aluminium was around 6 microns, and the average grain size of thetitanium carbonitride was around 1.5-2 microns. The diamond powder andnon-diamond phase mixture were mixed in a multidirectional Turbula mixerusing steel milling balls. After mixing, the powder was then placed intoa titanium cup and heated at 1025 degrees Celsius for a period beforebeing cooled and sieved to form a first phase mixture.

The first phase mixture was then attrition milled for around 4 hours inethanol media using a planetary ball mill with WC milling balls witharound 0.6 wt % organic dispersant such as Lubrizol™, cBN and diamondpowder having an average grain size of around 10 microns such that theratio of the diamond powder to non-diamond phase mixture was around60:40 vol %. After mixing, the powder was dried in a rota vapourapparatus. The dried powder was then dried and sieved to form apre-composite for the intermediate region.

In preparation of the components to form the PCD layer or region of thesuper hard construction, diamond powder with an average grain size ofabout 19 microns was mixed in a planetary ball mill for about 1 hourwith 1 wt % Co using methanol media and tungsten carbide milling balls.After mixing, the powder was sieved and dried in a rota vapour apparatusto remove the methanol and WC balls. The dried powder was then returnedto the planetary ball mill for about 5 minutes to remove agglomeratesbefore being sieved again.

The pre-composite for the intermediate region was then placed on top ofa cemented tungsten carbide substrate shaped to provide an interfacebetween the substrate and the intermediate region at least a portion ofwhich has an uneven topology. The substrate is also shaped to have arecess therein to receive both the pre-composite for the intermediateregion and the diamond powder to form the PCD layer, the substrateextending around the pre-composite for the intermediate region anddiamond powder acts as an infiltration source during the sinteringprocess for the sintering of the PCD layer.

About 1.4 grams of the prepared diamond power to form the PCD layer wasplaced on the pre-composite for the intermediate region to form apre-composite assembly. The assembly was then placed inside a refractorymetal can and the can assembly was exposed to a de-binding treatment at500 degrees Celsius under nitrogen and then vacuum heat treated andsealed at a temperature of around 1100° C. Subsequently the assembly wassealed and placed into a high pressure high temperature (HPHT)apparatus. The assembly was sintered at a pressure of around 8 GPa and atemperature of around 1550° C. for at least 30 seconds to form thecutter construction comprising an inter-bonded polycrystalline diamond(PCD) structure bonded to a substrate material through an intermediateregion formed of non-interbonded diamond grains and a matrix phase. Atleast some constituents in the pre-composite for the intermediate regionmelt during the HPHT sintering process. In some examples the sinteringtime was 20-40 minutes, and in some examples was a number of hours. Thediamond composite structure forming the intermediate region containedabout 60% by volume diamond and there was substantially no interbondingbetween the diamond grains in the diamond composite structure. Thematrix material of the intermediate region in this example wasdetermined to include one or more of TiCN, Al₂O₃, and Al₄C₃.

The cutter construction was recovered after sintering and fullyprocessed to a diameter of around 16 mm and an overall height of around13 mm with a PCD table thickness of about 1.3 mm separated from thesubstrate by the intermediate region formed of a diamond compositehaving a thickness of between around 0.7 mm to 0.85 mm. The intermediateregion formed of the diamond composite extended to the peripheral sideedge of the construction, the excess WC forming the substrate duringsintering having been removed to expose the peripheral side edge of thePCD layer and the intermediate region.

To render the PCD layer thermally stable, the super hard constructionwith the intermediate region and substrate attached was subjected to aboiling HCl acid leaching treatment for a number of hours until allaccessible residual catalysing material had been removed from theinterstitial spaces between inter-bonded diamond grains.

The materials used to form the intermediate region(s) in the variousexamples were separately tested to confirm that the super hard grains inthe material were non-intergrown (non-interbonded) and therefore werediamond composite materials in the examples and not considered to bepolycrystalline diamond (PCD) material. The tests performed includedvertical boring mill tests with two leached conventional polycrystallinediamond cutter elements formed of diamond grains having an average grainsize identical to the grain size in the respective diamond compositematerials and which were sintered under pressures of around 5.5 GPa. Theresults are shown in FIG. 11 and provide an indication of the total wearscar area plotted against cutting length. It was seen that the wearresistance of the diamond composite material denoted by referencenumeral 100 was at least three times less (ie worse) than that of theconventional PCD denoted by reference numerals 102, 104 which assistedin proving that the diamond composite materials were not intergrown andtherefore were not considered to be polycrystalline diamond materials.This was also evident from SEM and X-ray images of the structures whichshowed the diamond grains not to be inter-bonded (ie not inter-grown)and therefore not classed as PCD material.

The complete cutter construction itself was brazed to a steel toolholder and subjected to a vertical turret lathe test. The results areshown in FIGS. 12 and 13 .

It will be seen that the performance was significantly better than aconventional cutter formed of a PCD layer bonded to a WC substrate inwhich the PCD layer had the same average grain size as the PCD layer ofthe example and same PCD layer thickness that had not been subjected toan acid leaching treatment to remove all of the residual catalyst fromthe PCD region. The vertical turret lathe test was carried out at 50 RPMwith 0.2 mm depth of cut, a 20 degree negative back rake angle and a 6mm per revolution feed rate on Paarl granite rock. The results for thecutter construction of the example are shown in FIG. 12 and by referencenumeral 200 in the plot of FIG. 13 , the results for the conventionalPCD cutters being shown by reference numerals 202, 204 and 206 in theplot of FIG. 13 .

Whilst not wishing to be bound by a particular theory, it is believedthat in the examples the composition and structure of the intermediateregion provides a good support to the TS super hard structure,particularly as, for example, it is known that leaching conventional PCDtypically reduces the strength of the PCD by up to around 30%. Theintermediate region may be shaped to suit the particular end applicationof the super hard construction, for example, to ensure that a largesurface area of TS super hard material may be presented at the cuttingedge so that as the wear scar progresses, the wear is contained in theTS region which is supported by a tough and strong supportingintermediate region. In some examples, a protrusion from theintermediate region may have a higher impact resistance compared to thesuper hard layer and thereby act to assist in arresting cracks to avoidspalling or catastrophic failure during use of the super hardconstruction.

The size and shape of the intermediate region and the TS super hardregion may be tailored to the final application of the superhardmaterial. It is believed possible to improve spalling resistance withoutsignificantly compromising the overall abrasion resistance of thematerial, which is desirable for PCD and PCBN cutting tools.

Observation of the wear scar development during testing showed thematerial's ability to generate large wear scars without exhibitingbrittle-type micro-fractures (e.g. spalling or chipping), leading to alonger tool life.

Thus, examples of, for example, a PCD material, may be formed having acombination of high abrasion and fracture performance.

The super hard constructions may be finished by, for example, grinding,to provide a super hard element which is substantially cylindrical andhaving a substantially planar working surface, or a generally domed,pointed, rounded conical or frusto-conical working surface. The superhard element may be suitable for use in, for example, a rotary shear (ordrag) bit for boring into the earth, for a percussion drill bit or for apick for mining or asphalt degradation.

While various versions have been described with reference to a number ofexamples, those skilled in the art will understand that various changesmay be made and equivalents may be substituted for elements thereof andthat these examples are not intended to limit the particular versionsdisclosed. For example, to render the PCD thermally stable, the PCDstructure with the intermediate region attached may be subjected to acidto leach out catalyst material from between the diamond grains, or toother methods of achieving this, such as electrochemical methods.

The invention claimed is:
 1. A polycrystalline super hard constructioncomprising: a first region comprising a body of thermally stablepolycrystalline super hard material having an exposed surface forming aworking surface, and a peripheral side edge, said polycrystalline superhard material comprising a plurality of intergrown grains of super hardmaterial; a second region forming a substrate to the first region, thesecond region comprising a hard phase and a binder phase; a third regioninterposed between the first and second regions, the third regionextending across a surface of the second region along an interface;wherein the third region comprises a composite material having a firstphase comprising a plurality of non-intergrown diamond grains, and amatrix material; the polycrystalline super hard construction furthercomprising a fourth region interposed between the second region and thethird region, a major proportion of the fourth region comprising one ormore components of the binder material of the second region, the fourthregion further comprising one or more reaction products between thebinder material of the second region and one or more components of thethird region.
 2. The polycrystalline super hard construction of claim 1,wherein the third region extends across a surface of the fourth regionalong an interface, the interface, and the fourth region extends acrossa surface of the second region along an interface, one or other or bothof the interfaces comprising at least a portion having an uneventopology and/or a planar portion.
 3. The polycrystalline super hardconstruction of claim 1, wherein the composite material of the thirdregion further comprises a second phase.
 4. The polycrystalline superhard construction of claim 3, wherein the second phase comprises cBN,and/or WC, and/or wBN.
 5. The polycrystalline super hard construction ofclaim 3, wherein the second phase is formed of a material having ahardness less than the hardness of the first phase of the compositematerial.
 6. The polycrystalline super hard construction of claim 3,wherein the non-intergrown grains of super hard material and the secondphase of the composite material comprise between around 20 vol % toaround 95 vol % of the third region.
 7. The polycrystalline super hardconstruction of claim 1, wherein the matrix material of the third regioncomprises any one or more alloys or compounds of any one or moretransition metals including titanium, zirconium, vanadium, hafnium,tantalum, niobium, chromium, molybdenum, tungsten, copper, cobalt,nickel, iron, manganese, and rhenium.
 8. The polycrystalline super hardconstruction of claim 7, wherein the one or more alloys or compounds ofany one or more of the transition metals comprises oxides, nitrides,carbides, carbonitrides, and/or oxycarbides of said transition metals.9. The polycrystalline super hard construction of claim 1, wherein thematrix material of the third region comprises at least one of aluminium,nickel, and one or more alloys or compounds thereof.
 10. Thepolycrystalline super hard construction of claim 1, wherein the matrixmaterial of the third region comprises any one or more of titaniumcarbonitride, titanium diboride, aluminium nitride, aluminium oxide,cobalt, and tungsten carbide, or alloys or compounds thereof.
 11. Thepolycrystalline super hard construction of claim 1, wherein the matrixmaterial comprises between around 5 vol % to around 80 vol % of thethird region.
 12. The polycrystalline super hard construction of claim1, wherein the non-intergrown grains of super hard material of thecomposite material comprise between around 30 vol % to around 90 vol %of the third region.
 13. The polycrystalline super hard construction ofclaim 1, wherein the first region, the second region and the thirdregion each have an associated hardness, wherein the hardness of thethird region is greater than the hardness of the second region and lessthan the hardness of the first region.
 14. The polycrystalline superhard construction of claim 1, wherein the grains of super hard materialof the first region comprise diamond grains, the first region forming abody of polycrystalline diamond material.
 15. The polycrystalline superhard construction of claim 1, wherein the composite material of thethird region is more acid resistant than polycrystalline diamondmaterial having a binder-catalyst phase comprising cobalt, and/or moreacid resistant than cemented carbide material.
 16. The polycrystallinesuper hard construction of claim 15, wherein the composite material ofthe third region is more resistant to boiling HCl acid thanpolycrystalline diamond material having a binder-catalyst phasecomprising cobalt, and/or more resistant to boiling HCl acid thancemented carbide material.
 17. The super hard polycrystallineconstruction of claim 1, wherein the first region is substantially freeof a catalyst material for diamond.
 18. The super hard polycrystallineconstruction of claim 1, wherein the thermally stable first regioncomprises at most 3 weight percent of inaccessible catalyst material fordiamond.
 19. The super hard polycrystalline construction of claim 1,wherein the first region is bonded to the third region along anon-planar interface.
 20. The super hard polycrystalline construction ofclaim 1, wherein the construction has a longitudinal axis, the thicknessof the third region along a plane parallel to the longitudinal axisbeing between around 0.1 mm to around 4 mm.
 21. The super hardpolycrystalline construction of claim 1, wherein the third region has awear resistance at least three times less than sintered polycrystallinediamond material having the same average grain size of diamond grains asthe super hard grains in the third region.